Production blasting of Dc Beers Consolidated Mines Limited,
Koffiefontein and Finsch Mines involves both uphole trough rings of 9 to
I I holes and near vertical 360 degree compound rings of 42-54 holes.
The rate of production from these stages is dependent upon being able to
achieve a specified fragmentation size range and this has driven the
derivation of blasting practices to consistently achieve this target
fragmentation. At the Dutoitspan Mine, in Kimberley, where mining of the kimberlite
pipe is by block caving, 100 per cent extraction of the undercut level by
ring blasting is essential. If this is not achieved, pillars are formed which
not only inhibit the efficient initiation of the caving process, but also
concentrates load onto the extraction level, causing damage to draw
points and pillars. These two case studies demonstrate the importance of achieving
optimum blasting performance for downstream mining efficiency; ie
fragmentation for increased productivity at Koffiefontein Mine and 100
per cent undercut extraction for efficient initiation of the caving process at
the Dutoitspan Mine. The case studies also serve to highlight the long
road towards blast optimisation taken by De Beers Consolidated Mines
Ltd (Koffiefontein. Finsch, Premier and Kimberley Mines) since 1989.